Great Northern Paper is holding a celebration marking the one-year anniversary of the reopening of its East Millinocket mill. Great Northern Paper retirees, families and the public are invited to Thursday morning’s event at the mill. Cate Street Capital of Portsmouth, N.H., bought two shuttered paper mills in East Millinocket and Millinocket last September. It reopened the East Millinocket mill the following month, ultimately putting more than 250 people back to work and relaunching the historic Great Northern Paper brand. Cate Street is planning to build a wood pellet production facility on the site of the Millinocket mill, which closed in 2008. U.S. Rep. Mike Michaud and Maine Economic Development Commissioner George Gervais will attend the celebration, along with Cate Street Capital officials and local elected officials and business leaders.